A switching power supply device is used in various electronic machines since it can be downsized. When the switching power supply device is used to drive an electronic component such as CPU of which load current greatly varies, output voltage must be controlled to quickly recover a desired voltage when the load current varies.
As a conventional technique for performing such control, there has been proposed a technique in which a special current path is provided to supply/pull in current to/from an inductor or a capacitor forming a lowpass filter in the switching power supply device, when the load varies.
However, even when such a current path is provided, the output voltage changes depending on the load variation, and thus the variation in the output voltage cannot be restrained until the output voltage is set to a desired voltage.
Further, there is another conventional technique in which a plurality of current sources are connected to the output voltage line of the switching power supply device and one current source to be actually activated can be selected from these current sources depending on the load variation. However, since each current source operates at different timing, the output voltage eventually changes depending on the load variation and the variation in the output voltage cannot be restrained until the output voltage returns to a desired voltage.